Joachim H. Bürsch

Automated Video-Angiocardiographic Image Analysis

This paper describes a hardware-software system for handling the two main groups of cardiological data: a) physiological variables such as voltages, pressures, etc., and b) morphological data, derived from x-ray images or angiocardiograms, such as dimensions, areas, or volumes. We will concentrate in particular on some aspects of automated image processing–i. e., the analysis of the size, shape, and contraction pattern of the ventricles from video-angiocardiograms.

Computerized video-image preprocessing with applications to cardio-angiographic roentgen-image series

We report on the enhancement of video-angiocardiographic image-series by digital preprocessing methods including a newly developed technique of interframe subtraction recording as well as computerized image subtraction, integration, and nonlinear representation techniques. Background suppression and noise reduction obtained through these processes applied to roentgen images from animal experiments are demonstrated. Image-series handling and storage are simplified by combining a new method of digitally formatted videotape recording with conventional digital storage of selected image data in the periphery of a minicomputer system.

Use of digitized functional angiography to evaluate arterial blood flow

Digital angiography (DA), being a computer-based imaging system, allows for manipulation of the image data. One potential use derived from data manipulation is the production of functional images or images that reflect a physiologic parameter in addition to anatomic information. A discussion is presented of the background work employed to derive blood flow measurements using DA images, including the theoretical and practical limitations of the methodology. While absolute blood flow is hard to determine by any noninvasive and many invasive methods, flow velocity and relative blood flow in large vessels is obtainable with small vlumes of intraarterial contrast injection using the basic principles of indicator dilution techniques and evaluation of the time versus density relationships of contrast bolus. An appraisal of the functional imaging method is provided, including its drawbacks and the potential areas of application.

Intravenous Angiocardiography Using Digital Image Processing: 1. Experience with Axial Projections in Normal Pigs

Computerized digitization and processing of roentgen video images was performed in four-chamber-view intravenous angiocardiography in normal pigs. Significant contrast enhancement was obtained through electrocardiogram-gated background subtraction and rescaling after integration of multiple background and contrast images. Histogram equalization and time parameter extraction or functional imaging was also used. The left and right heart were well visualized after intravenous injection of 0.5-1 ml Urografin-76% per kg of body weight. Image processing of left and right ventricular end diastolic and end systolic frames was performed as well as subtraction of right and left end systolic from end diastolic frames and subtraction of right from left heart frames. If left ventricular end systolic images were subtracted from end diastolic images, the left ventricle was seen without continuity with the left atrium. Through time interval difference processing, left ventricular wall motion per time unit could be studied. The results were the basis for subsequent experiments concerning detection of septal defects in pigs as well as clinical studies.

Digital angiography in the diagnosis of congenital heart disease

Based on experimental and clinical studies, the technical aspects (choice of projection, injection technique), experimental and clinical results, and the indications for computerized digital angiography in congenital heart disease are reviewed. To obtain high-quality diagnostic images consistently, ECG-gating, suspended or gated respiration, and short pulsewidth acquistion are required. Clinically useful diagnostic information has been acquired in children with suspected functional murmurs, cardiac surgery that is believed to be inadequate, and in cyanotic newborns after intravenous injection of contrast material. Increased diagnostic information has also been obtained after intracardiac injection of small amounts of contrast and computerized digital processing of images in children undergoing cardiac catheterization.

Intravenous Angiocardiography Using Digital Image Processing II. Detection of Left-to-Right Shunts in an Animal Model

Digital image processing was applied in an experimental model to study the feasibility of intravenous angiocardiography for the detection of cardiac lesions with left-to-right shunting. Methods were designed to produce ventricular and atrial septal defects (VSD, ASD) as well as patent ductus arteriosus (PDA) equivalent in pigs. After intravenous (IV) injection of 0.5-1 ml of Urografin 76% per kg body weight, digitization and computerized processing of roentgen video images recorded at a rate of 50 fields per second was performed. The radiographic images were recorded in the four-chamber view obtained by 30-35 degrees of caudocranial angulation and 50-60 degrees of left anterior oblique positioning of the animal. The processing of images included electrocardiogramgated background subtraction, rescaling, and sometimes histogram equalization. Integration of multiple background and multiple contrast images was performed in order to increase the signal-to-noise ratio. Ventricular septal defects and patent ductus arteriosus could be detected per se, while atrial septal defect only could be indirectly detected. Respiratory motion artifacts could be avoided by cross-correlation respiratory gating or by subtracting left ventricular end systole from end diastole during the same cardiac cycle of left ventricular opacification. The results of the experiments in pigs are the basis for continued clinical use of digitized IV angiocardiography.

Assessment of left ventricular muscle volume by digital angiocardiography.

By means of digital image processing, the entire myocardial wall of the left ventricle could be visualized by biplanar angiocardiography in animal experiments using 14 pigs (weight, 16-25 kg). The resulting images of the myocardial wall allowed dimensional measurement by videometry. The muscle volume was computed according to Simpsons rule for end diastole and end systole and compared with postmortem measurements. Replication of the procedure resulted in a 95% confidence interval of +/- 11% (+/- 5.6 ml) at maximum. Comparison with postmortem data showed highly significant correlations of r = 0.894 (end diastole) and r = 0.938 (end systole). This study points out that digital image processing allows a reliable assessment of myocardial volume from routine left ventricular angiocardiography. Besides early clinical applications, the method has been successfully used to visualize nonperfused segments of the myocardial wall in artificial infarction.

Digital Videodensitometry: Some Approaches to Radiographic Image Restoration and Analysis

Videodensitometrie methods for the evaluation of blood flow and ventricular function have been developed in the past 15 years in parallel with cinedensitometry (Heintzen 1971; Heuck 1973; Heintzen and Bursch 1978). Recently, the successful application of digital image processing techniques in angiography (Brennecke et al. 1977; Kruger et al. 1978; Ovitt et al 1978) has increased the interest in video methods since they are directly compatible with digital electronic image processing systems. Digitization of the video signal brings the flexibility and reproducibility of computerized data processing to the field of densitometric analysis. Some of the degradations introduced by the imaging system can be eliminated by digital restoration techniques in order to improve the accuracy of image analysis.

Intravenous Angiocardiography Using Digital Image Processing: Experience With Axial Projections In Normal Pigs And In Pigs With Experimentally Generated Left-To-Right Shunts

Computerized digitization and processing of roentgen video images recorded at a rate of 50 per second was tested in intravenous angiocardiography in normal pigs weighing 15 to 20 kg. Roentgen video images were recorded in the 4-chamber view obtained by 30-35 degrees caudocranial angulation of the x-ray tube and 50-60 degrees LAO obliquity in the pig. Significant contrast enhancement was obtained through ECG-gated background subtraction and rescaling after integration of multiple background as well as contrast images. Occasionally, histogram equalization was used to further enhance contrast. To study temporal changes in cardiac motion, time parameter extraction or functional imaging was applied as well. The left and right heart were well visualized after intravenous injection of 1/3-1 cc. 76% Urografin per kg. bodyweight. Special purpose processing like subtraction of the end systolic phase from the end diastolic in the left and right ventricles as well as subtraction of the right ventricular phase from the left ventricular phase was also performed. If the left ventricular end systolic phase was subtracted from the end diastolic, most of the left atrium was also subtracted whereby the left ventricle was seen without continuity or superimposition of the left atrium. Experimentally generated ventricular and atrial septal defects as well as patent ductus arteriosus could be detected using the described technique. The results of the animal experiments became the basis for subsequent applications in children with congenital heart disease.

Present Status of Digital Angiocardiography

Conventional (“analog”) angiocardiography and angiography of the coronary and peripheral circulation provide fundamental information about structure and function of the cardiovascular system. These techniques have reached a very high level of perfection.